Method for manufacturing and inspecting blow-molded plastic containers

ABSTRACT

A method of manufacturing plastic containers. The method may comprise the steps of (1) forming a plastic container from a preform in a blow-molder, where the blow-molder comprises a plurality of molds and spindles; and (2) inspecting the plastic container after formation in the blow-molder. The containers are inspected by impinging infrared light thereon and detecting the portion of the infrared light that passes through the container and converting the same into corresponding electrical signals which are delivered to a microprocessor. The microprocessor receives signals from sensors associated with the blow-molder relating to the position of the molds, the identity of the molds and the identity of the spindles in order that the information that is determined by inspection can be associated with specific molds and spindles. The information may be visually displayed so as to provide feedback regarding the inspection process. In a preferred embodiment wall thickness measurements are taken at several vertically spaced positions simultaneously. Corresponding apparatus is provided.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/041,565, entitled “Method and apparatus for monitoring wallthickness of blow-molded plastic containers,” filed Jan. 24, 2005, whichis a continuation of U.S. patent application Ser. No. 10/106,263,entitled “Method and apparatus for monitoring wall thickness ofblow-molded plastic containers,” filed Mar. 26, 2002, now U.S. Pat. No.6,863,860.

BACKGROUND OF THE INVENTION

It has long been known that plastic containers such as bottles must beinspected in order to make sure that the wall thickness is adequate forthe desired purpose and that the use of excess material is minimized.

In general, it has been known to employ sampling inspection techniqueswherein, at a periodic intervals, which might be on the order of onceper hour, a container was removed from the conveyance system after thecontainer emerged from the blow-molder and was destructively tested bycutting the same into multiple, horizontal sections which were thenweighed with the weight being correlated with the wall thickness.

An alternative inspection method involved measuring the wall thicknessof such containers by nondestructively testing sample plasticcontainers. A suitable system for effecting such testing is the AGR TopWave Profiler Gauge PG 9800. A suitable laboratory instrument for thislatter approach is that sold under the trademark AGR Top Wave WallThickness Profiler. One of the problems with such an inspection approachis that it was time-consuming and labor intensive. Also, the longinterval between samplings resulted in a delay in process feedback whichin turn could result in reduced production efficiencies.

It has also been known to employ high-speed on-line wall thicknessmonitoring systems for blow-molded plastic containers. These systemsprovide real-time monitoring of material distributions and rejection ofdefects. A suitable system for such purpose is that sold under thetrademark AGR Top Wave PET Wall System. While these systems represent asubstantial improvement in the completeness of sampling by inspectingeach container and the timing of same, they did not provide feedbackcoordinated with the operation of the blow-molding machine.

U.S. Pat. No. 4,304,995 discloses a system for measuring wall thicknessof plastic containers employing infrared absorption. The containers aresampled off-line and required the use of rotation and disclosed the useof radiation sources and radiation detectors which were structured torotate with respect to each other.

U.S. Pat. No. 4,490,612 discloses a method of measuring the thickness ofplastic film using relative absorptions of two infrared wavelengths.

U.S. Pat. No. 5,139,406 discloses the use of infrared absorption inmeasuring the wall thickness of plastic containers. On-line measurementis contemplated, but this system requires insertion of a probe into thecontainer. Such an approach is uneconomical and inefficient in respectof current blow-molder plastic container production speeds.

U.S. Pat. No. 5,591,462 discloses the use of machine vision technologyin monitoring certain defects in blow-molded containers. Among thefeatures being monitored by this system are seal surface, base and neckfolds and finish gauge inspection.

PCT publication WO 01/65204 discloses a method and apparatus formeasuring plastic containers on-line employing infrared absorption. Theapparatus was said to be employable on a conveyer or inside theblow-molder. It made use of laterally homogenous material distributionproperties and measured though both sides of the container.

In spite of the foregoing prior art disclosures, there remains a veryreal and substantial need for an improved inspection system for blowmolded plastic containers which will provide timely and accuratefeedback regarding not only whether a container fell within the wallthickness specifications, but also identity of the molds and associatedspindles which produced the container.

SUMMARY OF THE INVENTION

In one general aspect, the present invention directed to a methodinvolving the inspection of the wall thickness of blow-molded plasticcontainers by providing a plastic container blow-molder having aplurality of molds and a plurality of associated spindles. Thecontainers are inspected by impinging infrared light thereon anddetecting the portion of the infrared light that passes though thecontainer and converting the same to corresponding electrical signalswhich are delivered to a microprocessor. The microprocessor receives thethickness related signals and compares them with stored informationregarding the desired thickness and emits thickness information. Avisual display of such information, which may include an averagecontainer wall thickness over a period of time, for each mold andspindle may be provided.

The method may involve providing a plurality of such systems so thatcontainer wall thickness may be measured substantially simultaneously ata plurality of elevations.

The method includes sensing a plurality of conditions in theblow-molder, including mold position, mold identity and spindle identitysuch that the thickness determined can be synchronized with a particularmold and spindle to thereby provide meaningful feedback regarding thethickness determination.

The presence of a container to be inspected in the inspection station isalso provided. A reject mechanism for physically removing a rejectedcontainer is also provided.

In another general aspect, the present invention is directed to anapparatus for inspecting blow-molded plastic containers. The apparatusmay include an inspection station preferably disposed inside of theblow-molder and having at least one source of infrared radiation whichimpinges the radiation on the plastic container to be inspected andcooperating photodetectors which may be photoconductive lead-sulfideinfrared detectors, for example. These receive the infrared radiationpassing through the container and convert the same into correspondingelectrical signals which are delivered to the microprocessor. Themicroprocessor contains stored information regarding the desiredthickness and is structured to effect a comparison and issue thicknessinformation output signals which may go to a visual display unit forpresentation to an operator and may also, if the container is to berejected, present such a signal to the reject mechanism which willremove the container from the line. Sensors for sensing the moldassembly position, as well as the identity of each mold and spindle soas to synchronize the same with the container being inspected areprovided and are preferably disposed within the blow-molder.

In another general aspect, the present invention is directed to a methodof manufacturing plastic containers. The method may comprise the stepsof (1) forming a plastic container from a preform in a blow-molder,where the blow-molder comprises a plurality of molds and spindles; and(2) inspecting the plastic container after formation in the blow-molder.The step of inspecting the plastic container may comprise directinglight energy from at least one light energy source from an exterior ofthe plastic container toward the plastic container after formation ofthe plastic container by the blow-molder and sensing, with at least onelight energy sensor operatively associated with the at least one lightenergy source, a portion of the light energy that passes through theplastic container. The step of inspecting may also comprise generating asignal from the sensed portion of the light energy that passes throughthe plastic container that is related to the light energy absorbed bythe plastic container and inputting the signal related to the lightenergy absorbed by the plastic container to a microprocessor. The stepof inspecting may also comprise inputting, to the microprocessor, atleast one timing signal indicative of the mold and spindle of theblow-molder involved in the formation of the plastic container. The stepof inspecting may also comprise determining, by the microprocessor, acontainer attribute of the plastic container based on the signal relatedto the light energy absorbed by the plastic container and determining,by the microprocessor, the mold and spindle of the blow-molder involvedin forming the plastic container based on the at least one timingsignal.

According to various implementations, the container attribute may be thesidewall thickness of the plastic container. Also, the manufacturingmethod may also comprise adjusting a parameter of the blow-molder basedon the inspection. Further, the method may also comprise rejecting theplastic container if it does not pass the inspection by separating theplastic container from non-rejected plastic containers. In addition, themethod may comprise visually displaying information about the inspectionon a display. The displayed information may include informationassociating the container attribute with identification of the mold andspindle involved in the formation of the plastic container.

It is an object of the present invention to provide an improvedautomated on-line rapid inspection system for inspecting wall thicknessof plastic containers, such as bottles, for example.

It is another object of the invention to provide a method an apparatusfor effecting such inspection while providing meaningful feedbackregarding the specific mold and spindle which made a given container.

It is another object of the present invention to provide such a systemwhich employs sensors within the blow-molder to provide information to amicroprocessor regarding mold position and mold and spindle identity asrelated to a specific blow-molded container.

It is an object of the present invention to provide a system which isadapted for rapid on-line assembly of plastic bottles and other plasticcontainers made by blow-molding in such a manner as to identify the moldand spindle which made a specific container.

It is a further object of the present invention to provide such a systemwhich will facilitate immediate communication of wall thicknessinformation for either manual or automated control of the blow-moldingsystem.

It is a further object of the invention to provide such a system whichenhances the efficiency of the manufacture of blow-molded plasticcontainers.

These and other objects of the present invention will be more fullyunderstood from the following description of the invention on referenceto the illustrations appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view showing the blow-molder, containertransporting mechanisms, the inspection area and reject area.

FIG. 2 is a perspective view showing a form of light source andassociated photodetector employable in the inspection station of thepresent invention.

FIG. 3 is a schematic diagram showing a form of apparatus usable in thepresent invention and the interaction of the same.

FIG. 4 is an algorithm flow chart illustrating the flow of informationin an embodiment of the present invention.

FIGS. 5( a), (b) and (c) illustrate a timing diagram showing therelationship among machine step, mold sync and spindle sync signals.

FIG. 6 illustrates a screen of a visual display unit employable in thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As employed herein, the term “containers” refers to plastic bottles,jars, vials and other plastic containers usable for storage of liquidand other flowable materials. Examples of the size of containers forwhich the present invention is particularly well suited are containershaving a capacity of about 0.2 to 3 liters.

In a typical prior art plastic container, blow-molding process preformsentering the blow-molder are typically at room temperature. The preformsare inverted and loaded, upside-down, onto spindles. The spindles carrythe preforms through the reheat oven which raises the temperature of theplastic in preparation for blow-molding. Uniform heating is important sothe spindles rotate as they traverse through the oven. There aretypically 100 to 400 spindles, forming a conveyor loop. After exitingthe reheat oven, the preforms are removed from the spindles andtransferred by a system of transfer wheels into the molds on the moldwheel. Failure of the spindles to rotate correctly while traversingthrough the oven will result in a poor thickness distribution in theblown container.

Employing one or more light sources of infrared radiation andcooperating associated photodetectors preferably located within theblow-molder near the output portion of a blow-molder where thecontainers are extracted from the molds, container wall thickness canreadily and rapidly be determined. It is known that plastic materialssuch as PET absorb infrared radiation of specific wavelengths. Thisfacilitates determination of the thickness of the container wall basedon the amount of infrared radiation that has been absorbed. In apreferred practice of the present invention, the thickness monitoringapparatus and method will employ two distinct infrared wavelengths inorder to compensate for refractive and scattering effects that mightotherwise have a deleterious effect on the measurement.

Referring to FIG. 1, a preform oven 2 typically carries the plasticpreforms on spindles through the oven section so as to preheat thepreforms prior to blow-molding of the containers. The preforms leavingthe preform oven 2 enter the mold assembly 6 which contains a pluralityof molds by means of conventional transfer apparatus 7 (shown inphantom). The blow-molder 4, which may be of conventional type, has thearray of molds which may be on the order of ten to twenty-four arrangedin a circle and rotating in a direction indicated by the arrow C.Containers emerging from the mold assembly 6, such as container 8, willbe suspended from a transfer arm, such as 10, on transfer assembly 12which is rotating in the direction indicated by arrow D. Similarly,transfer arms 14 and 16 will, as the transfer assembly 12 rotates, pickup a container such as 8 and transport it through the inspection area 20which will be described in greater detail hereinafter. A reject area 24has a reject mechanism 26 which will physically remove from the transferassembly 12 any containers deemed to be rejects. Container 30 has passedbeyond the reject area 24 and will be picked up in star wheel 34 whichis rotating in direction E and has a plurality of pockets, such as 36,38, 40, for example. Container 46 is shown as being present in such astar wheel pocket. The containers will then be transferred in a mannerknown to those skilled in the art to conveyer means according to thedesired transport path and nature of the system.

Referring to FIG. 2, there is shown a form of inspection station 20which has a container 60 passing therethrough in the direction indicatedby the arrow under the influence of a suitable conveyance device (notshown). In the form shown, a plurality of light sources 64, 66, 68 arevertically spaced from each other in order to inspect the wall thicknessof the bottle at three zones at three different elevations. Cooperatingwith the light sources 64, 66, 68, respectively, are photodetectors 74,76, 78. In operation, infrared radiation will be emitted by the lightsources 64, 66 68, impinge upon bottle 60, have a portion of theinfrared radiation absorbed by the plastic container 60 and have theremaining infrared radiation impinge upon the detectors 74, 76, 78 whichwill convert the received light into a corresponding electrical signalwhich will be delivered to a microprocessor for further processing. Anysuitable detector which will function efficiently with the infraredradiation wavelengths employed may be used. A preferred detector is aphotoconductive lead-sulfide (PbS) infrared detector. A suitable PbSdetector is that sold by CalSensors. In a preferred system, the detectorassembly consists of a prism-grating-prism spectrograph and two or morePbS detectors (such an assembly is manufactured by Spectral Imaging,Ltd. Of Finland, using PbS detectors from CalSensors). The spectrographdisperses the infrared radiation as a function of wavelength; thedetectors are located so as to be sensitive to specific wavelengths ofinfrared radiation. One wavelength is selected to correspond to anabsorption band in the plastic container. A second wavelength isselected to correspond to a transmission band in order to provide areference. As an alternative to using the spectrograph, band-passoptical filters may be used in conjunction with the PbS detectors.

Referring still to FIG. 2, further details regarding the creation ofsynchronized wall thickness determination as related to specific moldsand spindles will be considered. The light source preferably includes ahalogen bulb that is always on, a lens to collect and collimate thelight into a beam, a spinning segmented disk that “chops” the light beamand a remotely-controlled calibration disk. The light source ispreferably always “on,” emitting a pulsed beam (which preferably pulsesat about 600 Hz). The light source emits a pulsed beam of “white” light,containing all of the desired infrared wavelengths.

Referring to FIG. 3, there is shown a microprocessor 90 which, in theform shown, exercises control over the calibration disks, which arepreferably integral with light sources 92, 94, 96 and 98. A containerwhich will pass through the gap indicated generally as 100 will, in theform shown, receive light from sources 92, 94, 96 98, absorb a portionof the same and then have the light not absorbed impinge onphotodetector sensors 102, 104, 106 108, respectively, which willconvert the received light into corresponding electrical signals whichare delivered to the microprocessor 90.

In a preferred embodiment of the invention, three key sensors which arewithin or operatively associated with the blow molder, provideinformation to enable synchronization of the specific molds and spindleswhich made the container being inspected and thereby provide valuablefeedback information. One sensor, designated the blow-molder machinestep sensor 120, emits a signal which contains information regarding thecounting of the molds and spindles from their corresponding startingposition. The total number of molds or spindles may vary depending uponthe make and model of blow-molder, but this information is known inadvance. This information may be programmed into the system. A secondsignal, which is from the blow-molder synchronization sensor 122,provides information regarding start of a new cycle of rotating the moldassembly. The output of this sensor 122 is provided to microprocessor90. The blow-molder spindle synchronizing sensor 126 provides outputregarding the new cycle of rotating the spindle assembly. This output isprovided to the microprocessor 90. The sensors employed for monitoringmachine step mold sync and spindle sync may be positioned at anysuitable location within the blow-molder and may be of any suitabletype, such as inductive sensors which are well known to those skilled inthe art.

The part-in-place sensor 130 provides a signal to the computerindicating that a container has arrived at the inspection station andthat the wall thickness inspection should be initiated. At that point,the container transects the beams of white light containing all of thedesired infrared wavelengths emitted by light sources 92, 94, 96, 98.The system preferably employs an incandescent light bulb that isoperated in a continuous mode. This continuous light is preferablymechanically shuttered at the desired 600 Hz by a rotating segmenteddisk contained in the light source assembly. The output of the lightsource is a pulsed beam of light. This pulsed radiation is designed tomatch the characteristics of the detectors. The microprocessor 90receives the electrical signal and affects a comparison of the thicknessinformation contained within the electrical signal with storedinformation regarding desired thickness. If the thickness is not withinthe desired range, it emits a signal to the blow-molder reject 140 whichin turn initiates a rejection signal to operate rejection apparatus 24,26 (FIG. 1) and discard that container from the conveyer. The outputthickness information from the microprocessor 90 will be delivered totouchscreen display 150 which provides an operator with informationregarding specific containers produced by particular mold and spindlecombinations. It is preferred that the values be averaged over a periodof time which may be on the order of 30 seconds to ten minutes. Inaddition or in lieu of time measurement, the average may be obtained fora fixed number of containers which may be on the order of 2 to 2500. Theoperator also obtains trend information for the blow-molder andindividual molds and spindles through the visual display unit 150. Inthe event of serious problems requiring immediate attention, visualand/or audio alarms may be provided. As indicated by the dual arrows Fand G, an operator may input certain information to the microprocessor90 to alter calibrations in order to control operation of themicroprocessor. The operator may input process limits and reject limitsinto the microprocessor 90 for each of the thickness measurement zones.The reject limits are the upper and lower thickness values that wouldtrigger the rejection of a container. The process limits are the upperand lower values for the time-averaged or number of container averagedthickness that would trigger a process alarm indicator. Also, ifdesired, hard copy or other output of the microprocessor 90 results maybe provided as by output 152 which may be a conventional printer, forexample.

The microprocessor 90 display highlights molds or spindles havingundesirable thickness—either too thick or too thin. For example, if onemold was producing containers that are too thick or too thin, theoperator would adjust mold-related parameters such as blow-pressure orblow-rate to correct the problem; or the operator might need to stop theblow-molder to replace or repair an air valve for that mold. It will beappreciated that the mold/spindle-correlated feedback provided by themicroprocessor is used to localize the problem.

Referring to FIG. 4, an algorithm flow chart showing the method of theinspection process, container tracking and combining mold and spindleinformation of the present invention will be considered. As indicated inFIG. 3, the blow-molder machine step sensor 120 will provide an outputidentified in FIG. 4 as 180 and the blow-molder mold sync sensor 122will provide an output signal 182 and the blow-molder spindle syncsensor 126 will provide a spindle sync signal 186. As shown by block190, the machine step signal 180 contains information regarding theincremental movement of the mold module, the number of molds and theincremental spindle module and the number of spindles. The mold syncsignal 182 will verify that the mold is equal to the mold offset withresetting being accomplished if necessary.

In order to adjust for the fact that microprocessor 90 may start up inthe middle of a blow-molding cycle, the microprocessor 90 preferablyemploys an algorithm that allows the microprocessor to re-synchronizewith the blow-molder 4 within one mold or spindle cycle. Themicroprocessor 90 then remains synchronized with the blow-molder 4. Thealgorithm is:

-   -   Machine-step event: increment mold#, if mold# is greater than        number of molds, reset to 1 increment spindle#, if spindle# is        greater than number-of-spindles, reset to 1    -   Mold-sync event: Set mold# to X (mold offset as pre-configured)    -   Spindle-sync event: Set spindle# to Y (spindle offset as        pre-configured)

Similarly, the spindle sync signal 186 will verify that the spindleequals the spindle offset with a reset being achieved, if necessary. Thecollective output of blocks 190, 192 and 194 is detailed informationwith respect to the current mold and spindle identity and position withrespect to the container being inspected. The sensor 130 (FIG. 3), whena container has reached the inspection level will emit signal 210 whichis combined in block 212 by associating the specific mold and signalwith this particular container and this container is tracked insynchrony with the specific mold and spindle. In the next process block214, the microprocessor will collect and process the infrared sensordata, calculate the thickness and merge the results with thecorresponding container in the tracking queue.

The output of block 214 proceeds to block 216 where, if the container isbeing rejected, it is tracked to the rejection point and a decisionregarding pass and reject has been made.

Finally, the microprocessor in block 218 updates the container thicknesstrend database and communicates the thickness information to touchscreendisplay 150 (FIG. 3). This ends the tracking of that container. It willbe appreciated that the net result is that the particular containerbeing inspected is associated with a particular mold and associatedspindle with a reject or pass decision determining whether theparticular container remains in the conveying process or is excluded bythe reject mechanism. The information also serves to update thethickness trend database as displayed in unit 150 and printed orotherwise stored or processed in output unit 152 (FIG. 3).

Referring to FIG. 5, there is shown in FIG. 5(A) the machine step timingdiagram with there being a one-for-one correspondence between themachine step pulses and containers produced by the blow-molder. The moldsync pulse shown in FIG. 5(B) indicates the start of a new cycle of themold wheel assembly and the spindle-sync pulse as shown in FIG. 5(C)shows the start of a new cycle of the spindle loop.

At the inspection station, there is a fixed phase relationship betweenthe mold sync pulse and the machine step pulse corresponding to thefirst mold. This phase information, which may be referred to as the“MoldOffset,” is determined when the system is installed into theblow-molder and then is entered into the processor. Similarly, theSpindleOffset is determined during installation and entered into theprocess.

Referring to FIG. 6, there is shown a visual display screen 240 whichcould be presented on the touchscreen display unit 150 (FIG. 3) toprovide prompt and concise feedback regarding the mold/spindlecorrelated thickness information for purposes of process control andblow-molder optimization. The process status is shown in FIG. 6. Therepresentation on the left shows a container 250 which in the form shownis a bottle having an exteriorly threaded neck. The wall thickness hasbeen measured at vertically spaced levels 252, 254, 256. Each band 252,254, 256 will contain a numerical indication of the average wallthickness. These indicated numbers show the process-wide averagethickness at these measurement locations averaged over a certainselected period of time which may be on the order of 30 seconds to 10minutes or could be an average of a number of containers from about 2 to2500.

Referring still to FIG. 6, it is noted by way of example that band 252is subdivided into a plurality of units 255, 257, 259, 260, 262, each ofwhich may be presented in a distinctive color different from nextadjacent subportions of band 252 for ease of visual review. By way ofexample, the numbers underlying band 252 present a scale of thickness ininches taken to four decimal points. Overlying the band 252 appears thenumber 0.2088 with an inverted triangle pointing to a portion of band252. This number represents an average wall thickness at that locationof the bottle based on, for example, a period of time or a number ofcontainers measured. One seeing the computer screen 240, therefore, canquickly ascertain not only quantitatively what the average thicknessmeasurement has been, but also visually in terms of the position on thescale. Similar numerical scales and reading information would preferablybe contained on bands 254, 256.

On the right in FIG. 6 is a graphic representation of the mold wheelassembly 280 having each mold represented by a circle and containinginformation regarding the related container thickness. In the center ofthe mold circle, there is a grid 300 showing container thickness statusfor a number of spindles. As the number of spindles can be quite large,the display shows a pareto-optimized list of problem spindles with theidentity of the worst spindle problems being identified by a spindlenumber or other identifier.

With respect to the molds, it is noted that some indication regardingthickness may be provided by the use of different colors. For example,as shown, the number 290 points to a mold which has a whiterepresentation, as does 292. The remaining molds are shown in black. Asuitable scale may be provided so that the white indicates a thicknessabove or below control limits and the black indicates a thickness withinlimits. As these circles may contain numbers (not shown) identifying aparticular mold, this will enable an operator to obtain a visualindication regarding the average thickness as related to control limitsor reject limits for that mold. With regard to spindle representing grid300, as there are more spindles than shown in the grid, this embodimentwould employ the worst of the spindles in respect of containers whichhave been inspected and having the greatest departure from desired wallthickness. By way of example, the top row of squares identifiedrespectively by reference numbers 304, 306, 308, 310, 312, 314 areidentified respectively and related to spindles 1, 3, 12, 20, 21, 23. Asis true with the molds, these grid representations would preferably havecolor coding indicating as to each spindle in the grouping, the degreeof departure from the control limits or reject limits or, in the eventthat it is within limits, a color indicating that category. It will beappreciated that while the drawings show color representations for themolds as being black or white, and no color distinctions are provided inthe illustrated grid 300, two or more colors may be employed inrespective circles and blocks to indicate various thickness averages asrelated to the desired limits.

If desired, additional information may be provided on the screen 240.For example, if the average is based upon a time of 3 minutes, a legendto that effect may be provided. Similarly, if the average thickness isbased upon the last 250 bottles, a legend to this effect may beprovided. Also, information regarding the total number of rejects andthe percentage of rejects may be provided. Numerical indications of thenumber of rejects coming from each of the molds and spindles may also beprovided. The color codes or symbols such as “+” or “−” may be employedto identify whether the departure from desired control limits or rejectlimits are above or below such limits.

Where two distinct wavelengths of infrared radiation are used, a firstwill be at a wavelength which is readily absorbed by the plasticmaterial of the container and the other wavelength will be only slightlyabsorbed. A further possibility is that the containers may be filledwith condensed water vapor at the end of the blow-molding process. Ifthat is sufficiently dense, the internal fog formed in the container mayscatter light away from the sensors and interfere with measurement. Ifdesired, a third infrared wavelength which is not at an absorption bandwith respect to the plastic material can be used in order to calculate acorrection factor to enhance the accuracy of the thickness measurementby correcting for optical scattering caused by the fog.

It will be appreciated that the present invention has provided animproved automated system for wall thickness determination in a plasticcontainer which, as a result of sensors operatively associated with theblow-molder, provides detailed information so as to correlate wallthickness of a given container with the mold and spindle at which it ismade. The microprocessor processes data regarding the thicknessmeasurement and outputs the same to a unit which may visually displayand/or to another unit which may provide hard copy of the averagethickness readings which may also be a thickness reading achieved over aperiod of time such as about 30 seconds to 10 minutes or a number ofcontainers which may be about 2 to 2500.

1. A method of manufacturing a plastic container comprising: forming theplastic container from a preform in a blow-molder, the blow-moldercomprising a plurality of molds and spindles; and inspecting the plasticcontainer after formation in the blow-molder, wherein inspecting theplastic container comprises: directing light energy from at least onelight energy source from an exterior of the plastic container toward theplastic container after formation of the plastic container by theblow-molder; sensing with at least one light energy sensor operativelyassociated with the at least one light energy source a portion of thelight energy that passes through the plastic container, wherein the atleast one light energy source and the at least one light energy sensorare located in the blow-molder; generating a signal from the sensedportion of the light energy that passes through the plastic containerthat is related to the light energy absorbed by the plastic container;inputting the signal related to the light energy absorbed by the plasticcontainer to a microprocessor; inputting, to the microprocessor, atleast one timing signal indicative of the mold and spindle of theblow-molder involved in the formation of the plastic container;determining, by the microprocessor, a container attribute of the plasticcontainer based on the signal related to the light energy absorbed bythe plastic container; and determining, by the microprocessor, the moldand spindle of the blow-molder involved in forming the plastic containerbased on the at least one timing signal.
 2. The method of claim 1,wherein the container attribute is average sidewall thickness.
 3. Themethod of claim 1, further comprising adjusting a parameter of theblow-molder based on the inspection.
 4. The method of claim 1 furthercomprising automatically rejecting the plastic container if it does notpass the inspection by separating the plastic container fromnon-rejected plastic containers.
 5. The method of claim 1, furthercomprising visually displaying information about the inspection on adisplay.
 6. The method of claim 5, wherein the displayed informationcomprises information associating the container attribute withidentification of the mold and spindle involved in the formation of theplastic container.
 7. The method of claim 1, wherein the step ofdetermining the container attribute of the plastic container based onthe signal related to the light energy absorbed by the plastic containercomprises determining whether the container attribute is within desiredlimits based on the amount of light energy absorbed by the container. 8.The method of claim 1, wherein the step of directing light energy fromthe at least one energy source from the exterior of the plasticcontainer toward the plastic container comprises directing light energyfrom the at least one energy source from the exterior of the plasticcontainer toward the plastic container while the plastic container issuspended in an inspection area.
 9. The method of claim 8, wherein thestep of directing light energy from the at least one energy source fromthe exterior of the plastic container toward the plastic containercomprises directing light energy from the at least one energy sourcefrom the exterior of the plastic container toward the plastic containerwhile the plastic container is suspended in the inspection area by atransfer arm.
 10. The method of claim 9, wherein the transfer armcomprises a rotating transfer arm.
 11. The method of claim 10, furthercomprising adjusting a parameter of the blow-molder based on theinspection.
 12. The method of claim 8, further comprising adjusting aparameter of the blow-molder based on the inspection.
 13. A method ofinspecting a plastic container formed by a blow-molder, wherein theblow-molder includes a plurality of molds for forming the plasticcontainer, the method comprising: directing light energy from at leastone light energy source from an exterior of the plastic container towardthe plastic container after formation of the plastic container by theblow-molder; sensing with at least one light energy sensor operativelyassociated with the at least one light energy source a portion of thelight energy that passes through the plastic container, wherein the atleast one light energy source and the at least one light energy sensorare located in the blow-molder; generating a signal from the sensedportion of the light energy that passes through the plastic containerthat is related to the light energy absorbed by the plastic container;inputting the signal related to the light energy absorbed by the plasticcontainer to a microprocessor; inputting, to the microprocessor, atleast one timing signal indicative of the mold of the blow-molderinvolved in the formation of the plastic container; determining, by themicroprocessor, a container attribute of the plastic container based onthe signal related to the light energy absorbed by the plasticcontainer; and determining, by the microprocessor, the mold of theblow-molder involved in formation of the plastic container based on theat least one timing signal.
 14. The method of claim 13, furthercomprising adjusting a parameter of the blow-molder based on theinspection.
 15. The method of claim 13 further comprising automaticallyrejecting the plastic container if it does not pass the inspection byseparating the plastic container from non-rejected plastic containers.16. The method of claim 13, further comprising visually displayinginformation about the inspection on a display.
 17. The method of claim16, wherein the displayed information comprises information associatingthe container attribute with identification of the mold involved in theformation of the plastic container.
 18. The method of claim 13, whereinthe step of determining the container attribute of the plastic containerbased on the signal related to the light energy absorbed by the plasticcontainer comprises determining whether the container attribute iswithin desired limits based on the amount of light energy absorbed bythe container.
 19. The method of claim 13, wherein the step of directinglight energy from the at least one energy source from the exterior ofthe plastic container toward the plastic container comprises directinglight energy from the at least one energy source from the exterior ofthe plastic container toward the plastic container while the plasticcontainer is suspended in an inspection area.
 20. The method of claim19, wherein the step of directing light energy from the at least oneenergy source from the exterior of the plastic container toward theplastic container comprises directing light energy from the at least oneenergy source from the exterior of the plastic container toward theplastic container while the plastic container is suspended in theinspection area by a transfer arm.
 21. The method of claim 20, whereinthe transfer arm comprises a rotating transfer arm.
 22. The method ofclaim 21, further comprising adjusting a parameter of the blow-molderbased on the inspection.
 23. The method of claim 19, further comprisingadjusting a parameter of the blow-molder based on the inspection.
 24. Anapparatus for inspecting a plastic container formed by a blow-molder,wherein the blow-molder includes a plurality of molds for forming theplastic container, the apparatus comprising: at least one light energysource for directing light energy from an exterior of the plasticcontainer toward the plastic container after formation of the plasticcontainer by the blow-molder; at least one light energy sensoroperatively associated with the at least one light energy source forsensing a portion of the light energy that passes through of the plasticcontainer and generating a signal from the sensed portion of the lightenergy that passes through the plastic container that is related to thelight energy absorbed by the plastic container; and a microprocessor incommunication with the at least one light energy sensor for: determininga container attribute of the plastic container based on the signalrelated to the light energy absorbed by the plastic container; anddetermining the mold involved in formation of the plastic containerbased on at least one timing signal received by the microprocessor,wherein the at least one timing signal is indicative of the moldinvolved in the formation of the plastic container, and wherein: the atleast one light energy source is for directing light energy having twodistinct infrared wavelengths toward the plastic container; and the atleast one light energy sensor is for sensing, for each of the twodistinct infrared wavelengths, the portion of the light energy thatpasses through the sidewalls of the plastic container.
 25. The apparatusof claim 24, further comprising a reject mechanism in communication withthe microprocessor for rejecting the plastic container when themicroprocessor determines that the container attribute is not within aspecified range.
 26. The apparatus of claim 24, wherein the containerattribute includes the thickness of the sidewalls of the plasticcontainer.
 27. The apparatus of claim 24, further comprising a displayin communication with the microprocessor for displaying informationcorrelating the container attribute to the mold involved in forming theplastic container.
 28. The apparatus of claim 24, wherein: the at leastone light energy source includes at least two vertically aligned lightenergy sources; and the at least one light energy sensor includes threeat least two vertically aligned light energy sensors cooperativelyassociated with a corresponding one of the light energy sources.
 29. Theapparatus of claim 28, wherein the at least two light energy sensorscomprise non-imaging sensors.
 30. The apparatus of claim 24, wherein theat least one light energy source is positioned on a first side of atransport path for the plastic container and the at least one lightenergy sensor is on the opposite side of the transport path such thatthe plastic container passes between the at least one light energysource and the at least one light energy sensor.
 31. The apparatus ofclaim 24, wherein the at least one timing signal includes a signaltransmitted to the microprocessor by at least one of: a blow-moldermachine step sensor; and a blow-molder mold synchronization sensor. 32.The apparatus of claim 24, wherein the at least one energy source is fordirecting light energy from the exterior of the plastic container towardthe plastic container while the plastic container is suspended in aninspection area.
 33. The apparatus of claim 32, wherein the at least oneenergy source is for directing light energy from the exterior of theplastic container toward the plastic container while the plasticcontainer is suspended in the inspection area by a transfer arm.
 34. Theapparatus of claim 33, wherein the transfer arm comprises a rotatingtransfer arm.
 35. The apparatus of claim 32, wherein the microprocessoris further for determining whether the container attribute is withindesired limits based on the amount of light energy absorbed by thecontainer.
 36. An apparatus for inspecting a plastic container formed bya blow-molder, wherein the blow-molder includes a plurality of molds forforming the plastic container, the apparatus comprising: at least threevertically aligned light energy sources for directing light energy froman exterior of the plastic container toward the plastic container afterformation of the plastic container by the blow-molder; at least threevertically aligned light energy sensors cooperatively associated with acorresponding one of the light energy sources for sensing a portion ofthe light energy that passes through of the plastic container andgenerating a signal from the sensed portion of the light energy thatpasses through the plastic container that is related to the light energyabsorbed by the plastic container; and a microprocessor in communicationwith the at least one three light energy sensors for: determining acontainer attribute of the plastic container based on the signal relatedto the light energy absorbed by the plastic container; and determiningthe mold involved in formation of the plastic container based on atleast one timing signal received by the microprocessor, wherein the atleast one timing signal is indicative of the mold involved in theformation of the plastic container.
 37. An apparatus comprising: ablow-molder comprising a plurality of molds and spindles for forming aplastic container from a preform; an inspection device, located in theblow-molder, for inspecting the plastic container after formation by theblow-molder, wherein the inspection device comprises: at least one lightenergy source for directing light energy from an exterior of the plasticcontainer toward the plastic container after formation of the plasticcontainer by the blow-molder; at least one light energy sensoroperatively associated with the at least one light energy source forsensing a portion of the light energy that passes through of the plasticcontainer and generating a signal from the sensed portion of the lightenergy that passes through the plastic container that is related to thelight energy absorbed by the plastic container; and a microprocessor incommunication with the inspection device for: determining a containerattribute of the plastic container based on the signal related to thelight energy absorbed by the plastic container; and determining the moldinvolved in formation of the plastic container based on at least onesensor signal received by the microprocessor.
 38. The apparatus of claim37, wherein: the at least one light energy source comprises at least twovertically aligned light energy sources; and the at least one lightenergy sensor comprises at least two vertically aligned light energysources cooperatively associated with a corresponding one of the lightenergy sources.
 39. The apparatus of claim 38, wherein the light energysources comprises infrared light energy sources.
 40. The apparatus ofclaim 39, wherein the light energy sensors comprise non-imaging sensors.41. The apparatus of claim 39, wherein: the at least two verticallyaligned, infrared light energy sources are positioned on a first side ofa transport path for the plastic container; and the at least twovertically aligned light energy sensors are on an opposite side of thetransport path such that the plastic container passes between the atleast two light energy sources and the at least two light energysensors.
 42. The apparatus of claim 41, further comprising a transferarm in the blow molder for transporting the plastic container along thetransport path through the inspection device.
 43. The apparatus of claim42, wherein: each of the at least two vertically, aligned infrared lightenergy sources are for directing light energy having two distinctinfrared wavelengths toward the plastic container; and each of the atleast two vertically aligned light energy sensors are for sensing, foreach of the two distinct infrared wavelengths, the portion of the lightenergy that passes through the sidewalls of the plastic container. 44.The apparatus of claim 42, wherein the microprocessor is further fordetermining whether the container attribute is within desired limitsbased on the amount of light energy absorbed by the container.
 45. Theapparatus of claim 44, further comprising a display in communicationwith the microprocessor for displaying information correlating thecontainer attribute to the mold involved in forming the plasticcontainer.
 46. The apparatus of claim 45, wherein the microprocessor isfurther for determining the spindle involved in formation of the plasticcontainer based on the at least one sensor signal received by themicroprocessor.
 47. The apparatus of claim 46, wherein the at least onesensor signal includes a signal transmitted to the microprocessor fromthe blow molder.
 48. The apparatus of claim 47, wherein the at least onesensor signal includes at least one of: a blow-molder machine stepsensor; and a blow-molder mold synchronization sensor.
 49. An apparatuscomprising: a blow-molder comprising a plurality of molds and spindlesfor forming a plastic container from a preform; a transfer arm assemblyin the blow-molder for transporting the plastic container along atransport path after formation by the blow-molder an inspection device,located in the blow-molder, for inspecting the plastic container alongthe transport path after formation by the blow-molder, wherein theinspection device comprises: at least two vertically aligned lightenergy sources on a first side of the transport path for directing lightenergy from an exterior of the plastic container toward the plasticcontainer after formation of the plastic container by the blow-molder;at least two vertically aligned light energy sensors on a second side ofthe transport path opposite the first side, each of the at least twolight energy sensors operatively associated with one of the at least twolight energy sources, wherein the at least two light energy sensors arefor sensing a portion of the light energy that passes through twosidewalls of the plastic container and generating signals from thesensed portion of the light energy that passes through the two sidewallsof the plastic container that is related to the light energy absorbed bythe two sidewalls of the plastic container; and a microprocessor incommunication with the inspection device for: determining whether acontainer attribute of the plastic container based on the signalsrelated to the light energy absorbed by the plastic container is withindesired limits; and determining the mold involved in formation of theplastic container based on at least one sensor signal received by themicroprocessor.
 50. The apparatus of claim 49, wherein themicroprocessor is further for determining the spindle involved information of the plastic container based on the at least one sensorsignal received by the microprocessor.
 51. A method of manufacturing aplastic container comprising: forming the plastic container from apreform in a blow-molder, the blow-molder comprising a plurality ofmolds and spindles; transporting the plastic container with a transferalong a transport path through an inspection station after formation ofthe plastic container by the blow-molder; and inspecting the plasticcontainer as it passes through the inspection station, whereininspecting the plastic container comprises: directing light energy froman exterior of the plastic container toward the plastic container fromat least two vertically arranged light energy sources on a first side ofthe transport path; sensing with at least two vertically arranged lightenergy sensors a portion of the light energy that passes through twosidewalls of the plastic container, wherein each of the light energysensors are operatively associated with one of the at least two lightenergy sources, wherein the at least two light energy sources and the atleast two light energy sensors are located in the blow-molder;generating signals from the sensed portion of the light energy thatpasses through the two sidewalls of the plastic container that isrelated to the light energy absorbed by the two sidewalls of the plasticcontainer; inputting signals related to the light energy absorbed by theplastic container to a microprocessor; inputting, to the microprocessor,at least one sensor signal indicative of the mold involved in theformation of the plastic container; determining, by the microprocessor,whether a container attribute of the plastic container based on thesignals related to the light energy absorbed by the plastic container iswithin desired limits; and determining, by the microprocessor, the moldof the blow-molder involved in forming the plastic container based onthe at least one sensor signal.
 52. The method of claim 51, furthercomprising adjusting a parameter of the blow-molder based on theinspection.
 53. The method of claim 52, further comprising, determining,by the microprocessor the spindle of the blow-molder involved in formingthe plastic container based on the at least one sensor signal.